Cortical spreading depression causes and coincides with tissue hypoxia

Efficacy of Tricaine (MS-222) and Hypothermia as Anesthetic Agents for Blocking Sensorimotor Responses in Larval Zebrafish

Tricaine, or MS-222, is the most commonly used chemical anesthetic in zebrafish research. It is thought to act via blocking voltage-gated sodium channels, though its mechanism of action, particularly at the neuronal level, is not yet fully understood. Here, we first characterized the effects of tricaine on both body balance and touch responses in freely swimming animals, before determining its effect on the neural activity underlying the optokinetic response at the level of motion perception, sensorimotor signaling and the generation of behavior in immobilized animals. We found that the standard dose for larvae (168 mg/L) induced loss of righting reflex within 30 seconds, which then recovered within 3 minutes. Optokinetic behavior recovered within 15 minutes. Calcium imaging showed that tricaine interferes with optokinetic behavior by interruption of the signals between the pretectum and hindbrain. The motion sensitivity indices of identified sensory neurons were unchanged in larvae exposed to tricaine, though fewer such neurons were detected, leaving a small population of active sensory neurons. We then compared tricaine with gradual cooling, a potential non-chemical alternative method of anesthesia. While neuronal tuning appeared to be affected in a similar manner during gradual cooling, gradual cooling induced a surge in calcium levels in both the pretectum and hindbrain. This calcium surge, alongside a drop in heartrate, is potentially associated with harmful changes in physiology and suggests that tricaine is a better anesthetic agent than gradual cooling for zebrafish laboratory research.

Spreading depolarizations in ischaemia after subarachnoid haemorrhage, a diagnostic phase III study

Focal brain damage after aneurysmal subarachnoid haemorrhage predominantly results from intracerebral haemorrhage, and early and delayed cerebral ischaemia. The prospective, observational, multicentre, cohort, diagnostic phase III trial, DISCHARGE-1, primarily investigated whether the peak total spreading depolarization-induced depression duration of a recording day during delayed neuromonitoring (delayed depression duration) indicates delayed ipsilateral infarction. Consecutive patients (n = 205) who required neurosurgery were enrolled in six university hospitals from September 2009 to April 2018. Subdural electrodes for electrocorticography were implanted. Participants were excluded on the basis of exclusion criteria, technical problems in data quality, missing neuroimages or patient withdrawal (n = 25). Evaluators were blinded to other measures. Longitudinal MRI, and CT studies if clinically indicated, revealed that 162/180 patients developed focal brain damage during the first 2 weeks. During 4.5 years of cumulative recording, 6777 spreading depolarizations occurred in 161/180 patients and 238 electrographic seizures in 14/180. Ten patients died early; 90/170 developed delayed infarction ipsilateral to the electrodes. Primary objective was to investigate whether a 60-min delayed depression duration cut-off in a 24-h window predicts delayed infarction with >0.60 sensitivity and >0.80 specificity, and to estimate a new cut-off. The 60-min cut-off was too short. Sensitivity was sufficient [= 0.76 (95% confidence interval: 0.65-0.84), P = 0.0014] but specificity was 0.59 (0.47-0.70), i.e. <0.80 (P < 0.0001). Nevertheless, the area under the receiver operating characteristic (AUROC) curve of delayed depression duration was 0.76 (0.69-0.83, P < 0.0001) for delayed infarction and 0.88 (0.81-0.94, P < 0.0001) for delayed ischaemia (reversible delayed neurological deficit or infarction). In secondary analysis, a new 180-min cut-off indicated delayed infarction with a targeted 0.62 sensitivity and 0.83 specificity. In awake patients, the AUROC curve of delayed depression duration was 0.84 (0.70-0.97, P = 0.001) and the prespecified 60-min cut-off showed 0.71 sensitivity and 0.82 specificity for reversible neurological deficits. In multivariate analysis, delayed depression duration (β = 0.474, P < 0.001), delayed median Glasgow Coma Score (β = -0.201, P = 0.005) and peak transcranial Doppler (β = 0.169, P = 0.016) explained 35% of variance in delayed infarction. Another key finding was that spreading depolarization-variables were included in every multiple regression model of early, delayed and total brain damage, patient outcome and death, strongly suggesting that they are an independent biomarker of progressive brain injury. While the 60-min cut-off of cumulative depression in a 24-h window indicated reversible delayed neurological deficit, only a 180-min cut-off indicated new infarction with >0.60 sensitivity and >0.80 specificity. Although spontaneous resolution of the neurological deficit is still possible, we recommend initiating rescue treatment at the 60-min rather than the 180-min cut-off if progression of injury to infarction is to be prevented.

Microglia Modulate Cortical Spreading Depolarizations After Ischemic Stroke: A Narrative Review

Cortical spreading depolarizations (CSDs) are characterized by waves of diminished electroencephalography activity that propagate across the cortex with subsequent loss of ionic homeostasis. CSDs have been found in many pathological conditions, including migraine, traumatic brain injury, and ischemic stroke. Because of CSD-associated ionic and metabolic disturbances at the peri-infarct area after ischemic stroke, it is thought that CSDs exacerbate tissue infarction and worsen clinical outcomes. Microglia, the main innate immune cells in the brain, are among the first responders to brain tissue damage. Recent studies demonstrated that microglia play a critical role in CSD initiation and propagation. In this article, we discuss the significance of CSD in the setting of ischemic stroke and how microglia may modulate peri-infarct CSDs, also known as iso-electric depolarizations. Finally, we discuss the significance of microglial Ca²⁺ and how it might be used as a potential therapeutic target for patients with ischemic stroke.

Mutated neuronal voltage-gated CaV2.1 channels causing familial hemiplegic migraine 1 increase the susceptibility for cortical spreading depolarization and seizures and worsen outcome after experimental traumatic brain injury

Patients suffering from familial hemiplegic migraine type 1 (FHM1) may have a disproportionally severe outcome after head trauma, but the underlying mechanisms are unclear. Hence, we subjected knock-in mice carrying the severer S218L or milder R192Q FHM1 gain-of-function missense mutation in the CACNA1A gene that encodes the α_1A subunit of neuronal voltage-gated Ca_V2.1 (P/Q-type) calcium channels and their wild-type (WT) littermates to experimental traumatic brain injury (TBI) by controlled cortical impact and investigated cortical spreading depolarizations (CSDs), lesion volume, brain edema formation, and functional outcome. After TBI, all mutant mice displayed considerably more CSDs and seizures than WT mice, while S218L mutant mice had a substantially higher mortality. Brain edema formation and the resulting increase in intracranial pressure were more pronounced in mutant mice, while only S218L mutant mice had larger lesion volumes and worse functional outcome. Here, we show that gain of Ca_V2.1 channel function worsens histopathological and functional outcome after TBI in mice. This phenotype was associated with a higher number of CSDs, increased seizure activity, and more pronounced brain edema formation. Hence, our results suggest increased susceptibility for CSDs and seizures as potential mechanisms for bad outcome after TBI in FHM1 mutation carriers.

Validating a Computational Framework for Ionic Electrodiffusion with Cortical Spreading Depression as a Case Study

Cortical spreading depression (CSD) is a wave of pronounced depolarization of brain tissue accompanied by substantial shifts in ionic concentrations and cellular swelling. Here, we validate a computational framework for modeling electrical potentials, ionic movement, and cellular swelling in brain tissue during CSD. We consider different model variations representing wild-type (WT) or knock-out/knock-down mice and systematically compare the numerical results with reports from a selection of experimental studies. We find that the data for several CSD hallmarks obtained computationally, including wave propagation speed, direct current shift duration, peak in extracellular K+ concentration as well as a pronounced shrinkage of extracellular space (ECS) are well in line with what has previously been observed experimentally. Further, we assess how key model parameters including cellular diffusivity, structural ratios, membrane water and/or K+ permeabilities affect the set of CSD characteristics.

Migraine Aura, Transient Ischemic Attacks, Stroke, and Dying of the Brain Share the Same Key Pathophysiological Process in Neurons Driven by Gibbs–Donnan Forces, Namely Spreading Depolarization

Neuronal cytotoxic edema is the morphological correlate of the near-complete neuronal battery breakdown called spreading depolarization, or conversely, spreading depolarization is the electrophysiological correlate of the initial, still reversible phase of neuronal cytotoxic edema. Cytotoxic edema and spreading depolarization are thus different modalities of the same process, which represents a metastable universal reference state in the gray matter of the brain close to Gibbs–Donnan equilibrium. Different but merging sections of the spreading-depolarization continuum from short duration waves to intermediate duration waves to terminal waves occur in a plethora of clinical conditions, including migraine aura, ischemic stroke, traumatic brain injury, aneurysmal subarachnoid hemorrhage (aSAH) and delayed cerebral ischemia (DCI), spontaneous intracerebral hemorrhage, subdural hematoma, development of brain death, and the dying process during cardio circulatory arrest. Thus, spreading depolarization represents a prime and simultaneously the most neglected pathophysiological process in acute neurology. Aristides Leão postulated as early as the 1940s that the pathophysiological process in neurons underlying migraine aura is of the same nature as the pathophysiological process in neurons that occurs in response to cerebral circulatory arrest, because he assumed that spreading depolarization occurs in both conditions. With this in mind, it is not surprising that patients with migraine with aura have about a twofold increased risk of stroke, as some spreading depolarizations leading to the patient percept of migraine aura could be caused by cerebral ischemia. However, it is in the nature of spreading depolarization that it can have different etiologies and not all spreading depolarizations arise because of ischemia. Spreading depolarization is observed as a negative direct current (DC) shift and associated with different changes in spontaneous brain activity in the alternating current (AC) band of the electrocorticogram. These are non-spreading depression and spreading activity depression and epileptiform activity. The same spreading depolarization wave may be associated with different activity changes in adjacent brain regions. Here, we review the basal mechanism underlying spreading depolarization and the associated activity changes. Using original recordings in animals and patients, we illustrate that the associated changes in spontaneous activity are by no means trivial, but pose unsolved mechanistic puzzles and require proper scientific analysis.

Physiological variables in association with spreading depolarizations in the late phase of ischemic stroke

Physiological effects of spreading depolarizations (SD) are only well studied in the first hours after experimental stroke. In patients with malignant hemispheric stroke (MHS), monitoring of SDs is restricted to the postoperative ICU stay, typically day 2-7 post-ictus. Therefore, we investigated the role of physiological variables (temperature, intracranial pressure, mean arterial pressure and cerebral perfusion pressure) in relationship to SD during the late phase after MHS in humans. Additionally, an experimental stroke model was used to investigate hemodynamic consequences of SD during this time window. In 60 patients with MHS, the occurrence of 1692 SDs was preceded by a decrease in mean arterial pressure (-1.04 mmHg; p = .02) and cerebral perfusion pressure (-1.04 mmHg; p = .03). Twenty-four hours after middle cerebral artery occlusion in 50 C57Bl6/J mice, hypothermia led to prolonged SD-induced hyperperfusion (+2.8 min; p < .05) whereas hypertension mitigated initial hypoperfusion (-1.4 min and +18.5%Δ rCBF; p < .01). MRI revealed that SDs elicited 24 hours after experimental stroke were associated with lesion progression (15.9 vs. 14.8 mm³; p < .01). These findings of small but significant effects of physiological variables on SDs in the late phase after ischemia support the hypothesis that the impact of SDs may be modified by adjusting physiological variables.

Cortical spreading depression and meningeal nociception

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CSD evoked persistent activation and mechanical sensitization of dural nociceptors is likely to drive the headache phase in migraine with aura.

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The development of neurogenic-mediated dural vasodilatation and increased plasma protein extravasation in the wake of CSD may not contribute to meningeal nociception.

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Cortical vasoconstriction and reduced oxygen availability following CSD do not contribute to meningeal nociception.

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Cortical neuroinflammation, involving neuronal pannexin1 and calcium-independent astrocytic signaling drive meningeal nociception following CSD.

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CSD-related closing of K(ATP) channels and release of COX-driven prostanoids mediate the activation and sensitization of dural nociceptors respectively.

Migraine results in an enormous burden on individuals and societies due to its high prevalence, significant disability, and considerable economic costs. Current treatment options for migraine remain inadequate, and the development of novel therapies is severely hindered by the incomplete understanding of the mechanisms responsible for the pain. The sensory innervation of the cranial meninges is now considered a key player in migraine headache genesis. Recent studies have significantly advanced our understanding of some of the processes that drive meningeal nociceptive neurons, which may be targeted therapeutically to abort or prevent migraine pain. In this review we will summarize our current understanding of the mechanisms that contribute to the genesis of the headache in one migraine subtype – migraine with aura. We will focus on animal studies that address the notion that cortical spreading depression is a critical process that drives meningeal nociception in migraine with aura, and discuss recent insights into some of the proposed underlying mechanisms.

The Critical Role of Spreading Depolarizations in Early Brain Injury: Consensus and Contention

BACKGROUND

When a patient arrives in the emergency department following a stroke, a traumatic brain injury, or sudden cardiac arrest, there is no therapeutic drug available to help protect their jeopardized neurons. One crucial reason is that we have not identified the molecular mechanisms leading to electrical failure, neuronal swelling, and blood vessel constriction in newly injured gray matter. All three result from a process termed spreading depolarization (SD). Because we only partially understand SD, we lack molecular targets and biomarkers to help neurons survive after losing their blood flow and then undergoing recurrent SD.

METHODS

In this review, we introduce SD as a single or recurring event, generated in gray matter following lost blood flow, which compromises the Na⁺/K⁺ pump. Electrical recovery from each SD event requires so much energy that neurons often die over minutes and hours following initial injury, independent of extracellular glutamate.

RESULTS

We discuss how SD has been investigated with various pitfalls in numerous experimental preparations, how overtaxing the Na⁺/K⁺ ATPase elicits SD. Elevated K⁺ or glutamate are unlikely natural activators of SD. We then turn to the properties of SD itself, focusing on its initiation and propagation as well as on computer modeling.

CONCLUSIONS

Finally, we summarize points of consensus and contention among the authors as well as where SD research may be heading. In an accompanying review, we critique the role of the glutamate excitotoxicity theory, how it has shaped SD research, and its questionable importance to the study of early brain injury as compared with SD theory.

Translational Stroke Research Review: Using the Mouse to Model Human Futile Recanalization and Reperfusion Injury in Ischemic Brain Tissue

The approach to reperfusion therapies in stroke patients is rapidly evolving, but there is still no explanation why a substantial proportion of patients have a poor clinical prognosis despite successful flow restoration. This issue of futile recanalization is explained here by three clinical cases, which, despite complete recanalization, have very different outcomes. Preclinical research is particularly suited to characterize the highly dynamic changes in acute ischemic stroke and identify potential treatment targets useful for clinical translation. This review surveys the efforts taken so far to achieve mouse models capable of investigating the neurovascular underpinnings of futile recanalization. We highlight the translational potential of targeting tissue reperfusion in fully recanalized mouse models and of investigating the underlying pathophysiological mechanisms from subcellular to tissue scale. We suggest that stroke preclinical research should increasingly drive forward a continuous and circular dialogue with clinical research. When the preclinical and the clinical stroke research are consistent, translational success will follow.

Neuronal Activity in the Sciatic Nerve Is Accompanied by Immediate Cytoskeletal Changes

Mechanical events and alterations in neuronal morphology that accompany neuronal activity have been observed for decades. However, no clear neurophysiological role, nor an agreed molecular mechanism relating these events to the electrochemical process, has been found. Here we hypothesized that intense, yet physiological, electrical activity in neurons triggers cytoskeletal depolymerization. We excited the sciatic nerve of anesthetized mice with repetitive electric pulses (5, 10, and 100 Hz) for 1 and 2 min and immediately fixed the excised nerves. We then scanned the excised nerves with high-resolution transmission electron microscopy, and quantified cytoskeletal changes in the resulting micrographs. We demonstrate that excitation with a stimulation frequency that is within the physiological regime is accompanied by a significant reduction in the density of cytoskeletal proteins relative to the baseline values recorded in control nerves. After 10 Hz stimulation with durations of 1 and 2 min, neurofilaments density dropped to 55.8 and 51.1% of the baseline median values, respectively. In the same experiments, microtubules density dropped to 23.7 and 38.5% of the baseline median values, respectively. These changes were also accompanied by a reduction in the cytoskeleton-to-cytoplasm contrast that we attribute to the presence of depolymerized electron-dense molecules in the lumen. Thus, we demonstrate with an in vivo model a link between electrical activity and immediate cytoskeleton rearrangement at the nano-scale. We suggest that this cytoskeletal plasticity reduces cellular stiffness and allows cellular homeostasis, maintenance of neuronal morphology and that it facilitates in later stages growth of the neuronal projections.

Inverse neurovascular coupling and associated spreading depolarization models for traumatic brain injury

The paper presents the mathematical model of cortical spreading depolarisation and its effect on inverse neurovascular coupling. The paper considers the potassium ion channels present in the neuron-astrocyte blood vascular network to access the role of potassium ions during spreading depolarisation and associated inverse neurovascular coupling. Simulation of our proposed mathematical model confirms the experimental results that an increase in concentration of potassium ions beyond 20mM in the perivascular space essentially leads to vasoconstriction and hence inverse neurovascular coupling. The propagatory nature of depolarizing potassium waves has been unraveled though our proposed mathematical model.

Oxygen-Induced and pH-Induced Direct Current Artifacts on Invasive Platinum/Iridium Electrodes for Electrocorticography

BACKGROUND

Spreading depolarization (SD) and the initial, still reversible phase of neuronal cytotoxic edema in the cerebral gray matter are two modalities of the same process. SD may thus serve as a real-time mechanistic biomarker for impending parenchyma damage in patients during neurocritical care. Using subdural platinum/iridium (Pt/Ir) electrodes, SD is observed as a large negative direct current (DC) shift. Besides SD, there are other causes of DC shifts that are not to be confused with SD. Here, we systematically analyzed DC artifacts in ventilated patients by observing changes in the fraction of inspired oxygen. For the same change in blood oxygenation, we found that negative and positive DC shifts can simultaneously occur at adjacent Pt/Ir electrodes.

METHODS

Nurses and intensivists typically increase blood oxygenation by increasing the fraction of inspired oxygen at the ventilator before performing manipulations on the patient. We retrospectively identified 20 such episodes in six patients via tissue partial pressure of oxygen (p_tiO₂) measurements with an intracortical O₂ sensor and analyzed the associated DC shifts. In vitro, we compared Pt/Ir with silver/silver chloride (Ag/AgCl) to assess DC responses to changes in pO₂, pH, or 5-min square voltage pulses and investigated the effect of electrode polarization on pO₂-induced DC artifacts.

RESULTS

Hyperoxygenation episodes started from a p_tiO₂ of 37 (30-40) mmHg (median and interquartile range) reaching 71 (50-97) mmHg. During a total of 20 episodes on each of six subdural Pt/Ir electrodes in six patients, we observed 95 predominantly negative responses in six patients, 25 predominantly positive responses in four patients, and no brain activity changes. Adjacent electrodes could show positive and negative responses simultaneously. In vitro, Pt/Ir in contrast with Ag/AgCl responded to changes in either pO₂ or pH with large DC shifts. In response to square voltage pulses, Pt/Ir falsely showed smaller DC shifts than Ag/AgCl, with the worst performance under anoxia. In response to pO₂ increase, Pt/Ir showed DC positivity when positively polarized and DC negativity when negatively polarized.

CONCLUSIONS

The magnitude of pO₂-induced subdural DC shifts by approximately 6 mV was similar to that of SDs, but they did not show a sequential onset at adjacent recording sites, could be either predominantly negative or positive in contrast with the always negative DC shifts of SD, and were not accompanied by brain activity depression. Opposing polarities of pO₂-induced DC artifacts may result from differences in baseline electrode polarization or subdural p_tiO₂ inhomogeneities relative to subdermal p_tiO₂ at the quasi-reference.

Neurovascular dynamics of repeated cortical spreading depolarizations after acute brain injury

Cortical spreading depolarizations (CSDs) are increasingly suspected to play an exacerbating role in a range of acute brain injuries, including stroke, possibly through their interactions with cortical blood flow. We use simultaneous wide-field imaging of neural activity and hemodynamics in Thy1-GCaMP6f mice to explore the neurovascular dynamics of CSDs during and following Rose Bengal-mediated photothrombosis. CSDs are observed in all mice as slow-moving waves of GCaMP fluorescence extending far beyond the photothrombotic area. Initial CSDs are accompanied by profound vasoconstriction and leave residual oligemia and ischemia in their wake. Later, CSDs evoke variable responses, from constriction to biphasic to vasodilation. However, CSD-evoked vasoconstriction is found to be more likely during rapid, high-amplitude CSDs in regions with stronger oligemia and ischemia, which, in turn, worsens after each repeated CSD. This feedback loop may explain the variable but potentially devastating effects of CSDs in the context of acute brain injury.

Zhao et al. use wide-field optical mapping of neuronal and hemodynamic activity in mice, capturing CSDs immediately following photothrombosis. Initial CSDs are accompanied by strong vasoconstriction, leaving persistent oligemia and ischemia. Region-dependent neurovascular responses to subsequent CSDs demonstrate a potential vicious cycle of CSD-dependent damage in acute brain injury.

Case Report: Retinal Infarction Associated with Migraine

SIGNIFICANCE

Retinal migraine and migrainous infarction are distinct clinical entities delineated by the International Headache Society. Presented is a novel case report demonstrating unique optical coherence tomography evidence of retinal ischemia experienced during a migraine with effects across retinal vascular territories. This may represent evidence of migrainous infarction within the retina.

PURPOSE

The purpose of this study is to present clinical and quasi-histologic optical coherence tomography features of retinal ischemia associated with migraine.

CASE REPORT

Presented is a case of profound monocular vision loss coincident with a migraine episode. Optical coherence tomography with novel features of acute inner retinal thinning, increased delineation of the inner plexiform and outer plexiform layers, and increased signal intensity of the photoreceptor layer is reported. These discriminating characteristics contrast those of retinal artery occlusions and other primary ocular vasculopathies such as Susac syndrome and acute macular neuroretinopathies.

CONCLUSIONS

A case of permanent vision loss with retinal thinning and ischemic hyperreflectivity of retinal layers on optical coherence tomography in different vascular territories is shown to be associated with migraine. These features may provide clinical evidence of migrainous pathophysiology within the retina.

The efficacy of alpha-lipoic acid in improving oxidative, inflammatory, and mood status in women with episodic migraine in a randomised, double-blind, placebo-controlled clinical trial

AIM

Migraine is a common neurovascular disorder, which is associated with severe to moderate disabling headaches. Oxidative stress and inflammation might play a role in migraine pathogenesis and the mood disorders. Considering the antioxidant and anti-inflammatory properties of alpha-lipoic acid (ALA), this study was designed to investigate its effect on oxidative, inflammatory, and mood conditions in women with episodic migraine.

METHODS

In total, 92 women with episodic migraine participated in the study. The patients were randomly divided into two groups, receiving a 300-mg capsule of ALA or placebo twice daily for 3 months. To assess the oxidative and inflammatory status, the serum levels of total antioxidant capacity (TAC), total oxidant status (TOS), glutathione (GSH), malondialdehyde (MDA), oxidative stress index (OSI), and C-reactive protein (CRP) were determined at the beginning and at the end of the intervention. A depression, anxiety, stress scale (DASS-21-items) questionnaire was used to evaluate mood status.

RESULTS

Finally, 79 patients reached the final analysis stage. At the end of the intervention, a significant decrease in the serum levels of MDA (means difference [MD]: -0.83, 95% confidence intervals (CI): -1.04, -0.62 nmol/mL vs MD: -0.32, CI: -0.48, -0.15 nmol/mL; P < .001) and CRP (MD: -0.78, CI: -1.17, -0.39 mg/L vs MD: -0.63, CI: -1.80, 0.52 mg/L; P < .001) was observed in the ALA as compared with the placebo group, but changes in serum GSH (P = .086), TAC (P = .068), TOS (P = .225), and OSI (P = .404) were not statistically significant. In addition, depression, anxiety, and stress (with P < .001, in all cases) had significantly decreased in the intervention as compared with the control group.

CONCLUSION

The results of this study suggest that ALA supplementation for 3 months has beneficial effects on improving the oxidative, inflammatory, and mood conditions of patients suffering from episodic migraine.

Optical coherence tomography of arteriolar diameter and capillary perfusion during spreading depolarizations

Spreading depolarization (SD) is associated with profound oligemia and reduced oxygen availability in the mouse cortex during the depolarization phase. Coincident pial arteriolar constriction has been implicated as the primary mechanism for the oligemia. However, where in the vascular bed the hemodynamic response starts has been unclear. To resolve the origin of the hemodynamic response, we used optical coherence tomography (OCT) to simultaneously monitor changes in the vascular tree from capillary bed to pial arteries in mice during two consecutive SDs 15 minutes apart. We found that capillary flow dropped several seconds before pial arteriolar constriction. Moreover, penetrating arterioles constricted before pial arteries suggesting upstream propagation of constriction. Smaller caliber distal pial arteries constricted stronger than larger caliber proximal arterioles, suggesting that the farther the constriction propagates, the weaker it gets. Altogether, our data indicate that the hemodynamic response to cortical SD originates in the capillary bed.

Pharmacological treatment of migraine: Drug classes, mechanisms of action, clinical trials and new treatments

Migraine is the sixth most prevalent disease globally, a major cause of disability, and it imposes an enormous personal and socioeconomic burden. Migraine treatment is often limited by insufficient therapy response, leading to the need for individually adjusted treatment approaches. In this review, we analyse historical and current pharmaceutical development approaches in acute and chronic migraine based on a comprehensive and systematic analysis of Food and Drug Administration (FDA)-approved drugs and those under investigation. The development of migraine therapeutics has significantly intensified during the last 3 years, as shown by our analysis of the trends of drug development between 1970 and 2020. The spectrum of drug targets has expanded considerably, which has been accompanied by an increase in the number of specialised clinical trials. This review highlights the mechanistic implications of FDA-approved and currently investigated drugs and discusses current and future therapeutic options based on identified drug classes of interest.

Experimental and Clinical Evidence of the Effectiveness of Riboflavin on Migraines

Riboflavin, a water-soluble member of the B-vitamin family, plays a vital role in producing energy in mitochondria and reducing inflammation and oxidative stress. Migraine pathogenesis includes neuroinflammation, oxidative stress, and mitochondrial dysfunction. Therefore, riboflavin is increasingly being recognized for its preventive effects on migraines. However, there is no concrete evidence supporting its use because the link between riboflavin and migraines and the underlying mechanisms remains obscure. This review explored the current experimental and clinical evidence of conditions involved in migraine pathogenesis and discussed the role of riboflavin in inhibiting these conditions. Experimental research has demonstrated elevated levels of various oxidative stress markers and pro-inflammatory cytokines in migraines, and riboflavin’s role in reducing these marker levels. Furthermore, clinical research in migraineurs showed increased marker levels and observed riboflavin’s effectiveness in reducing migraines. These findings suggest that inflammation and oxidative stress are associated with migraine pathogenesis, and riboflavin may have neuroprotective effects through its clinically useful anti-inflammatory and anti-oxidative stress properties. Riboflavin’s safety and efficacy suggests its usefulness in migraine prophylaxis; however, insufficient evidence necessitates further study.

Molecular mechanisms of brain water transport

Our brains consist of 80% water, which is continuously shifted between different compartments and cell types during physiological and pathophysiological processes. Disturbances in brain water homeostasis occur with pathologies such as brain oedema and hydrocephalus, in which fluid accumulation leads to elevated intracranial pressure. Targeted pharmacological treatments do not exist for these conditions owing to our incomplete understanding of the molecular mechanisms governing brain water transport. Historically, the transmembrane movement of brain water was assumed to occur as passive movement of water along the osmotic gradient, greatly accelerated by water channels termed aquaporins. Although aquaporins govern the majority of fluid handling in the kidney, they do not suffice to explain the overall brain water movement: either they are not present in the membranes across which water flows or they appear not to be required for the observed flow of water. Notably, brain fluid can be secreted against an osmotic gradient, suggesting that conventional osmotic water flow may not describe all transmembrane fluid transport in the brain. The cotransport of water is an unconventional molecular mechanism that is introduced in this Review as a missing link to bridge the gap in our understanding of cellular and barrier brain water transport.

The Role of Metabolism in Migraine Pathophysiology and Susceptibility

Migraine is a highly prevalent and disabling primary headache disorder, however its pathophysiology remains unclear, hindering successful treatment. A number of key secondary headache disorders have headaches that mimic migraine. Evidence has suggested a role of mitochondrial dysfunction and an imbalance between energetic supply and demand that may contribute towards migraine susceptibility. Targeting these deficits with nutraceutical supplementation may provide an additional adjunctive therapy. Neuroimaging techniques have demonstrated a metabolic phenotype in migraine similar to mitochondrial cytopathies, featuring reduced free energy availability and increased metabolic rate. This is reciprocated in vivo when modelling a fundamental mechanism of migraine aura, cortical spreading depression. Trials assessing nutraceuticals successful in the treatment of mitochondrial cytopathies including magnesium, coenzyme q10 and riboflavin have also been conducted in migraine. Although promising results have emerged from nutraceutical trials in patients with levels of minerals or vitamins below a critical threshold, they are confounded by lacking control groups or cohorts that are not large enough to be representative. Energetic imbalance in migraine may be relevant in driving the tissue towards maximum metabolic capacity, leaving the brain lacking in free energy. Personalised medicine considering an individual's deficiencies may provide an approach to ameliorate migraine.

Brain Energy Deficit as a Source of Oxidative Stress in Migraine: A Molecular Basis for Migraine Susceptibility

People with migraine are prone to a brain energy deficit between attacks, through increased energy demand (hyperexcitable brain) or decreased supply (mitochondrial impairment). However, it is uncertain how this precipitates an acute attack. Here, the central role of oxidative stress is adduced. Specifically, neurons' antioxidant defenses rest ultimately on internally generated NADPH (reduced nicotinamide adenine dinucleotide phosphate), whose levels are tightly coupled to energy production. Mitochondrial NADPH is produced primarily by enzymes involved in energy generation, including isocitrate dehydrogenase of the Krebs (tricarboxylic acid) cycle; and an enzyme, nicotinamide nucleotide transhydrogenase (NNT), that depends on the Krebs cycle and oxidative phosphorylation to function, and that works in reverse, consuming antioxidants, when energy generation fails. In migraine aura, cortical spreading depression (CSD) causes an initial severe drop in level of NADH (reduced nicotinamide adenine dinucleotide), causing NNT to impair antioxidant defense. This is followed by functional hypoxia and a rebound in NADH, in which the electron transport chain overproduces oxidants. In migraine without aura, a similar biphasic fluctuation in NADH very likely generates oxidants in cortical regions farthest from capillaries and penetrating arterioles. Thus, the perturbations in brain energy demand and/or production seen in migraine are likely sufficient to cause oxidative stress, triggering an attack through oxidant-sensing nociceptive ion channels. Implications are discussed for the development of new classes of migraine preventives, for the current use of C57BL/6J mice (which lack NNT) in preclinical studies of migraine, for how a microembolism initiates CSD, and for how CSD can trigger a migraine.

Neuronal complexity is attenuated in preclinical models of migraine and restored by HDAC6 inhibition

Migraine is the sixth most prevalent disease worldwide but the mechanisms that underlie migraine chronicity are poorly understood. Cytoskeletal flexibility is fundamental to neuronal-plasticity and is dependent on dynamic microtubules. Histone-deacetylase-6 (HDAC6) decreases microtubule dynamics by deacetylating its primary substrate, α-tubulin. We use validated mouse models of migraine to show that HDAC6-inhibition is a promising migraine treatment and reveal an undiscovered cytoarchitectural basis for migraine chronicity. The human migraine trigger, nitroglycerin, produced chronic migraine-associated pain and decreased neurite growth in headache-processing regions, which were reversed by HDAC6 inhibition. Cortical spreading depression (CSD), a physiological correlate of migraine aura, also decreased cortical neurite growth, while HDAC6-inhibitor restored neuronal complexity and decreased CSD. Importantly, a calcitonin gene-related peptide receptor antagonist also restored blunted neuronal complexity induced by nitroglycerin. Our results demonstrate that disruptions in neuronal cytoarchitecture are a feature of chronic migraine, and effective migraine therapies might include agents that restore microtubule/neuronal plasticity.

Trans-nasal high-flow dehumidified air in acute migraine headaches: A randomized controlled trial

BACKGROUND

Intranasal high flow of dehumidified (dry) air results in evaporative cooling of nasal passages. In this randomized clinical trial, we investigated the effect of dry gas induced nasal cooling on migraine headaches.

METHODS

In this single-blind study, acute migraineurs were randomized to either nasal high-flow dry oxygen, dry air, humidified oxygen or humidified air (control) at 15 L/min for 15 min. All gases were delivered at 37°C. Severity of headache and other migraine associated symptoms (International Classification for Headache Disorders, 3rd edition criteria) were recorded before and after therapy. The primary endpoint was change in pain scores, while changes in nausea, photosensitivity and sound sensitivity scores served as secondary endpoints. A linear regression model was employed to estimate the impact of individual treatment components and their individual interactions.

RESULTS

Fifty-one patients (48 ± 15 years of age, 82% women) were enrolled. When compared to the control arm (humidified air), all therapeutic arms showed a significantly greater reduction in pain scores (primary endpoint) at 2 h of therapy with dry oxygen (-1.6 [95% CI -2.3, -0.9]), dry air (-1.7 [95% CI -2.6, -0.7)]), and humidified oxygen (-2.3 [95% CI -3.5, -1.1]). A significantly greater reduction in 2-h photosensitivity scores was also noted in all therapeutic arms (-1.8 [95% CI -3.2, -0.4], dry oxygen; -1.7 [95% CI -2.9, -0.4], dry air; (-2.1 [95% CI -3.6, -0.6], humidified oxygen) as compared to controls. The presence of oxygen and dryness were independently associated with significant reductions in pain and photosensitivity scores. No adverse events were reported.

CONCLUSION

Trans-nasal high-flow dry gas therapy may have a role in reducing migraine associated pain.Clinical Trial registration: NCT04129567.

Cortical Spreading Depression Phenomena Are Frequent in Ischemic and Traumatic Penumbra: A Prospective Study in Patients With Traumatic Brain Injury and Large Hemispheric Ischemic Stroke

PURPOSE

Spreading depolarization (SD) phenomena are waves of neuronal depolarization, which propagate slowly at a velocity of 1 to 5 mm/minute and can occur in patients with ischemic or hemorrhagic stroke, traumatic brain injury, and migraine with aura. They form part of secondary injury, occurring after spreading ischemia. The purposes of this study were to describe the frequency and characteristics of SD phenomena and to define whether a correlation existed between SD and outcome in a group of patients with TBI and large hemispheric ischemic stroke.

METHODS

This was a prospective observational study of 39 adult patients, 17 with malignant middle cerebral artery infarction and 22 with moderate or severe traumatic brain injury, who underwent decompressive craniectomy and multimodal neuromonitoring including electrocorticography. Identification, classification, and interpretation of SDs were performed using the published recommendations from the Cooperative Study on Brain Injury Depolarization group. The outcomes assessed were functional disability at 6 and 12 months after injury, according to the extended Glasgow outcome scale, Barthel index, and modified Rankin scale.

RESULTS

Four hundred eighty-three SDs were detected, in 58.9% of the patients. Spreading depolarizations were more common, particularly the isoelectric SD type, in patients with malignant middle cerebral artery infarction (P < 0.04). In 65.21% of patients with SDs on electrocorticography, the "peak" day of depolarization was day 0 (the first 24 hours of recording). Spreading depolarization convulsions were present in 26.08% of patients with SDs. Patients with more SDs and higher depolarization indices scored worse on extended Glasgow outcome scale (6 months) and Barthel index (6 and 12 months) (P < 0.05).

CONCLUSIONS

Evidence on SD phenomena is important to ensure continued progress in understanding their pathophysiology, in the search for therapeutic targets to avoid additional damage from these secondary injuries.

Repeated mild traumatic brain injuries impair visual discrimination learning in adolescent mice

Cognitive deficits following a mild traumatic brain injury (mTBI) are common and are associated with learning deficits in school-age children. Some of these deficits include problems with long-term memory, working memory, processing speeds, attention, mental fatigue, and executive function. Processing speed deficits have been associated with alterations in white matter, but the underlying mechanisms of many of the other deficits are unclear. Without a clear understanding of the underlying mechanisms we cannot effectively treat these injuries. The goal of these studies is to validate a translatable touchscreen discrimination/reversal task to identify deficits in executive function following a single or repeated mTBIs. Using a mild closed skull injury model in adolescent mice we were able to identify clear deficits in discrimination learning following repeated injuries that were not present from a single mTBI. The repeated injuries were not associated with any deficits in motor-based behavior but did induce a robust increase in astrocyte activation. These studies provide an essential platform to interrogate the underlying neurological dysfunction associated with these injuries.

Rapid Neuronal Ultrastructure Disruption and Recovery during Spreading Depolarization-Induced Cytotoxic Edema

Two major pathogenic events that cause acute brain damage during neurologic emergencies of stroke, head trauma, and cardiac arrest are spreading depolarizing waves and the associated brain edema that course across the cortex injuring brain cells. Virtually nothing is known about how spreading depolarization (SD)-induced cytotoxic edema evolves at the ultrastructural level immediately after insult and during recovery. In vivo 2-photon imaging followed by quantitative serial section electron microscopy was used to assess synaptic circuit integrity in the neocortex of urethane-anesthetized male and female mice during and after SD evoked by transient bilateral common carotid artery occlusion. SD triggered a rapid fragmentation of dendritic mitochondria. A large increase in the density of synapses on swollen dendritic shafts implies that some dendritic spines were overwhelmed by swelling or merely retracted. The overall synaptic density was unchanged. The postsynaptic dendritic membranes remained attached to axonal boutons, providing a structural basis for the recovery of synaptic circuits. Upon immediate reperfusion, cytotoxic edema mainly subsides as affirmed by a recovery of dendritic ultrastructure. Dendritic recuperation from swelling and reversibility of mitochondrial fragmentation suggests that neurointensive care to improve tissue perfusion should be paralleled by treatments targeting mitochondrial recovery and minimizing the occurrence of SDs.

Migraine and aura triggered by normobaric hypoxia

BACKGROUND

For future experimental studies or the development of targeted pharmaceutical agents, a deeper insight into the pathophysiology of migraine is of utmost interest. Reliable methods to trigger migraine attacks including aura are desirable to study this complex disease in vivo.

METHODS

To investigate hypoxia as a trigger for migraine and aura, we exposed volunteers diagnosed with migraine, with (n = 16) and without aura (n = 14), to hypoxia utilizing a hypoxic chamber adjusted to a FiO₂ of 12.6%. The occurrence of headache, migraine, aura, and accompanying symptoms were registered and vital signs were collected for 6 hours under hypoxia and 2 hours of follow-up. A binary logistic regression analysis examined the probability of triggering headaches, migraines, aura, photo- and phonophobia.

FINDINGS

Of 30 participants, 24 (80.0%) developed headaches and 19 (63.3%) migraine, five (16.7%) reported aura. Two patients that developed aura never experienced aura symptoms before in their life. The increase of mean heart frequency was higher in patients developing headaches or migraine. Mean SpO₂ during hypoxia was 83.39%.

CONCLUSION

Hypoxia was able to trigger migraine attacks and aura independently of any pharmacological agent.

Migrainous Infarction and Cortical Spreading Depression

Migraine is a very common disorder of the nervous system. It shares similar physiological processes with stroke. Migrainous infarction is a rare complication of migraine with aura. The neuro-logical symptoms of migraine aura correspond to the cortical spreading depression and this depression can lead to a migrainous infarction. It is pertinent to state that the investigation and detection of the cortical depression might have a great clinical significance. Blood vessels in the cranium play an important role in the pathophysiology of migraine.  In the case of injured states of brain, the cortical spreading depression causes extreme vasoconstriction rather than vasodilation. The endothelial damage caused by the cortical spreading depression can result in hypercoagulability, leading to an increased risk of stroke. There are many genetic disorders in which migraine and stroke are the major symptoms and an insight into these disorders can help us in the understanding of complex mechanisms of migrainous infarction. It is pertinent to state that some derangements in the vascular function accompany migraine which may also serve as targets for research and treatment. This article will describe the hemodynamic and genetic relationship between migraine induced stroke and how it relates to the cortical spreading depression.

Structural and Functional Remodeling of the Brain Vasculature Following Stroke

Maintenance of cerebral blood vessel integrity and regulation of cerebral blood flow ensure proper brain function. The adult human brain represents only a small portion of the body mass, yet about a quarter of the cardiac output is dedicated to energy consumption by brain cells at rest. Due to a low capacity to store energy, brain health is heavily reliant on a steady supply of oxygen and nutrients from the bloodstream, and is thus particularly vulnerable to stroke. Stroke is a leading cause of disability and mortality worldwide. By transiently or permanently limiting tissue perfusion, stroke alters vascular integrity and function, compromising brain homeostasis and leading to widespread consequences from early-onset motor deficits to long-term cognitive decline. While numerous lines of investigation have been undertaken to develop new pharmacological therapies for stroke, only few advances have been made and most clinical trials have failed. Overall, our understanding of the acute and chronic vascular responses to stroke is insufficient, yet a better comprehension of cerebrovascular remodeling following stroke is an essential prerequisite for developing novel therapeutic options. In this review, we present a comprehensive update on post-stroke cerebrovascular remodeling, an important and growing field in neuroscience, by discussing cellular and molecular mechanisms involved, sex differences, limitations of preclinical research design and future directions.

Galvanic Redox Potentiometry Based Microelectrode Array for Synchronous Ascorbate and Single-Unit Recordings in Rat Brain

Neuronal communication relies on cooperation between the chemical and electrical patterns of neurons. Thus, techniques for illustrating the linkage of the neurochemical events and action potentials with high temporal and spatial resolution is imperative to gain a comprehensive understanding of the intricacies of brain function. Herein, we integrate galvanic redox potentiometry (GRP) and electrophysiological recording onto a 16-site Au microelectrode array (MEA), one of which is for indicating the ascorbate concentration while the others for single-unit activity assessment. The electrochemical probing site was modified with single-walled carbon nanotubes to promote electron-transfer kinetics of ascorbate at low overpotential so as to enlarge the driving force for the spontaneous ascorbate/O₂ cell reaction. The resulting GRP-based MEA outputs open-circuit potential that is in a linear relationship with the logarithmic ascorbate concentration and exhibits high selectivity against a set of coexisting electroactive species. Furthermore, no reciprocal interference between the two recording systems is observed during concurrent GRP sensing of ascorbate and single-unit recording in a rat brain. In vivo feasibility of the GRP-based MEA is demonstrated by synchronous real-time measurement of ascorbate release and electrical activity from multiple neuronal populations during spreading depression. Our GRP-based MEA sensor creates new opportunities to realize high-throughput screening or mapping of neurochemical patterns in a larger dimension and correlate them to neuron functions across a spatial scale.

A mathematical model for persistent post-CSD vasoconstriction

Cortical spreading depression (CSD) is the propagation of a relatively slow wave in cortical brain tissue that is linked to a number of pathological conditions such as stroke and migraine. Most of the existing literature investigates the dynamics of short term phenomena such as the depolarization and repolarization of membrane potentials or large ion shifts. Here, we focus on the clinically-relevant hour-long state of neurovascular malfunction in the wake of CSDs. This dysfunctional state involves widespread vasoconstriction and a general disruption of neurovascular coupling. We demonstrate, using a mathematical model, that dissolution of calcium that has aggregated within the mitochondria of vascular smooth muscle cells can drive an hour-long disruption. We model the rate of calcium clearance as well as the dynamical implications on overall blood flow. Based on reaction stoichiometry, we quantify a possible impact of calcium phosphate dissolution on the maintenance of F0F1-ATP synthase activity.

Therapeutic Implications of Altered Energy Metabolism in Migraine: A State-of-the-Art Review

Currently, the management strategies aimed at the resolution of migraine are pharmacological. Most of these therapies are known to alter the serotonin balance of the brain. Furthermore, therapies blocking the calcitonin gene-related peptide (CGRP) have also proven to be quite effective in their treatments. However, apart from being expensive, these therapies do not influence premonitory and aura symptoms. This suggests an incomplete approach and an inadequate understanding of the migraine pathophysiology. Recent metabolic studies have indicated that migraine should be considered as an adaptive response to the mismatch between the cerebral energy reserves and expenditure. Therefore, understanding the underlying metabolism helps derive possible novel therapeutic modalities for migraines. In this review, we highlight the underlying metabolic abnormalities found in migraine patients. This will form the basis of our evidence-based discussion on metabolic therapeutic options for migraines.

Migraine Pathophysiology

Migraine is the leading cause of years lost due to disability in individuals aged 15 to 49 years. Much has changed over the last three decades about our understanding of this complex neurological disorder. Various phases of migraine have been characterized and are the focus of this review. The premonitory phase involves bothersome symptoms experienced hours to days before migraine pain. Behavioral changes and functional neuroimaging studies point toward hypothalamic involvement during the premonitory and other migraine phases. Migraine aura is a disruptive, reversible neurological phenomenon that affects up to one-third of all migraineurs, and can overlap with the headache phase. The mechanism responsible for this phase is thought to be cortical spreading depolarization through the cortex. This process leads to temporary disruptions in ion homeostasis and the ensuing neuronal dysfunction. The headache phase involves activation of the trigeminocervical complex. Neuropeptides are implicated in trigeminal activation, and calcitonin gene-related peptide in particular has become a promising target of therapeutic intervention for migraine. The final phase of migraine is the postdrome, the period of time from the resolution of headache symptoms until return to baseline following a migraine. People often report neuropsychiatric, sensory, gastrointestinal, and general symptoms during this time, which can limit activity. Elucidating the neuroanatomical, chemical, and neuroimaging correlates of these migraine phases allows for an improved comprehension of the underlying changes associated with migraine symptomatology and can assist with evaluation of arising therapeutics for migraine management.

Flavin Adenine Dinucleotide Fluorescence as an Early Marker of Mitochondrial Impairment During Brain Hypoxia

Multimodal continuous bedside monitoring is increasingly recognized as a promising option for early treatment stratification in patients at risk for ischemia during neurocritical care. Modalities used at present are, for example, oxygen availability and subdural electrocorticography. The assessment of mitochondrial function could be an interesting complement to these modalities. For instance, flavin adenine dinucleotide (FAD) fluorescence permits direct insight into the mitochondrial redox state. Therefore, we explored the possibility of using FAD fluorometry to monitor consequences of hypoxia in brain tissue in vitro and in vivo. By combining experimental results with computational modeling, we identified the potential source responsible for the fluorescence signal and gained insight into the hypoxia-associated metabolic changes in neuronal energy metabolism. In vitro, hypoxia was characterized by a reductive shift of FAD, impairment of synaptic transmission and increasing interstitial potassium [K⁺]_o. Computer simulations predicted FAD changes to originate from the citric acid cycle enzyme α-ketoglutarate dehydrogenase and pyruvate dehydrogenase. In vivo, the FAD signal during early hypoxia displayed a reductive shift followed by a short oxidation associated with terminal spreading depolarization. In silico, initial tissue hypoxia followed by a transient re-oxygenation phase due to glucose depletion might explain FAD dynamics in vivo. Our work suggests that FAD fluorescence could be readily used to monitor mitochondrial function during hypoxia and represents a potential diagnostic tool to differentiate underlying metabolic processes for complementation of multimodal brain monitoring.

The role of Toll-like receptor signaling pathways in cerebrovascular disorders: the impact of spreading depolarization

Cerebral vascular diseases (CVDs) are a group of disorders that affect the blood supply to the brain and lead to the reduction of oxygen and glucose supply to the neurons and the supporting cells. Spreading depolarization (SD), a propagating wave of neuroglial depolarization, occurs in different CVDs. A growing amount of evidence suggests that the inflammatory responses following hypoxic-ischemic insults and after SD plays a double-edged role in brain tissue injury and clinical outcome; a beneficial effect in the acute phase and a destructive role in the late phase. Toll-like receptors (TLRs) play a crucial role in the activation of inflammatory cascades and subsequent neuroprotective or harmful effects after CVDs and SD. Here, we review current data regarding the pathophysiological role of TLR signaling pathways in different CVDs and discuss the role of SD in the potentiation of the inflammatory cascade in CVDs through the modulation of TLRs.

Dimethyl fumarate alleviates the nitroglycerin (NTG)-induced migraine in mice

Background

Oxidative stress and inflammatory pathways are involved in migraine and endogenous antioxidant defense system has a role in the prevention of hyperalgesia in migraine. In this study, we aimed to evaluate the role of the most pharmacologically effective molecules among the fumaric acid esters (FAEs), dimethyl fumarate, nuclear factor E2-related factor 2/antioxidant response element (Nrf-2/ARE) pathway-mediated, in regulating the hypersensitivity in a mouse model of nitroglycerine (NTG)-induced migraine.

Methods

Mice were orally administered with DMF at the doses of 10, 30, and 100 mg/kg, 5 min after NTG intraperitoneal injections. We performed histological and molecular analysis on the whole brain and behavioral tests after 4 h by NTG-migraine induction. The expression of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-кB) subunit p65, nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor alpha (IκBα), inducible nitrite oxide synthase (iNOS), cyclooxygenase 2 (COX-2), Nrf-2, manganese superoxide dismutase (Mn-SOD), and heme-oxygenase-1 (HO-1) were detected by Western blot. Tail flick, hot plate, orofacial formalin, and photophobia tests were used to evaluate migraine-like pain and migraine-related light sensitivity.

Moreover, we evaluate Nrf-2-dependent mechanism by the in vitro stimulation of cells extracted by trigeminal ganglia with diethylenetriamine/nitric oxide (DETA/NO), a nitric oxide (NO) donor. The cells were pre-treated with DMF and an antagonist of Nrf-2, trigonelline (TR) 2 h before DETA/NO stimulation.

Results

DMF treatment notably reduced histological damage as showed by cresyl violet staining; also, regulating both NF-κB and Nrf-2 pathway, DMF treatment decreased the severity of inflammation and increased the protective antioxidant action. Moreover, the headache was significantly reduced. The protective effect of DMF treatment, via Nrf-2, was confirmed in in vitro studies, through inhibition of Nrf-2 by trigonelline. Cytotoxicity, iNOS, and MnSOD expression were evaluated.

Conclusion

These results provided the evidence that DMF, by Nrf-2 modulation, has a protective effect on central sensitization induced by NTG, suggesting a new insight into the potential application of DMF as novel candidates in drug development for migraine.

Metabolism plays a central role in the cortical spreading depression: Evidence from a mathematical model

The slow propagating waves of strong depolarization of neural cells characterizing cortical spreading depression, or depolarization, (SD) are known to break cerebral homeostasis and induce significant hemodynamic and electro-metabolic alterations. Mathematical models of cortical spreading depression found in the literature tend to focus on the changes occurring at the electrophysiological level rather than on the ensuing metabolic changes. In this paper, we propose a novel mathematical model which is able to simulate the coupled electrophysiology and metabolism dynamics of SD events, including the swelling of neurons and astrocytes and the concomitant shrinkage of extracellular space. The simulations show that the metabolic coupling leads to spontaneous repetitions of the SD events, which the electrophysiological model alone is not capable to produce. The model predictions, which corroborate experimental findings from the literature, show a strong disruption in metabolism accompanying each wave of spreading depression in the form of a sharp decrease of glucose and oxygen concentrations, with a simultaneous increase in lactate concentration which, in turn, delays the clearing of excess potassium in extracellular space. Our model suggests that the depletion of glucose and oxygen concentration is more pronounced in astrocyte than neuron, in line with the partitioning of the energetic cost of potassium clearing. The model suggests that the repeated SD events are electro-metabolic oscillations that cannot be explained by the electrophysiology alone. The model highlights the crucial role of astrocytes in cleaning the excess potassium flooding extracellular space during a spreading depression event: further, if the ratio of glial/neuron density increases, the frequency of cortical SD events decreases, and the peak potassium concentration in extracellular space is lower than with equal volume fractions.

Direct electrophysiological evidence that spreading depolarization-induced spreading depression is the pathophysiological correlate of the migraine aura and a review of the spreading depolarization continuum of acute neuronal mass injury

Spreading depolarization is observed as a large negative shift of the direct current potential, swelling of neuronal somas, and dendritic beading in the brain's gray matter and represents a state of a potentially reversible mass injury. Its hallmark is the abrupt, massive ion translocation between intraneuronal and extracellular compartment that causes water uptake (= cytotoxic edema) and massive glutamate release. Dependent on the tissue's energy status, spreading depolarization can co-occur with different depression or silencing patterns of spontaneous activity. In adequately supplied tissue, spreading depolarization induces spreading depression of activity. In severely ischemic tissue, nonspreading depression of activity precedes spreading depolarization. The depression pattern determines the neurological deficit which is either spreading such as in migraine aura or migraine stroke or nonspreading such as in transient ischemic attack or typical stroke. Although a clinical distinction between spreading and nonspreading focal neurological deficits is useful because they are associated with different probabilities of permanent damage, it is important to note that spreading depolarization, the neuronal injury potential, occurs in all of these conditions. Here, we first review the scientific basis of the continuum of spreading depolarizations. Second, we highlight the transition zone of the continuum from reversibility to irreversibility using clinical cases of aneurysmal subarachnoid hemorrhage and cerebral amyloid angiopathy. These illustrate how modern neuroimaging and neuromonitoring technologies increasingly bridge the gap between basic sciences and clinic. For example, we provide direct electrophysiological evidence for the first time that spreading depolarization-induced spreading depression is the pathophysiological correlate of the migraine aura.

Spreading Depolarizations Occur in Mild Traumatic Brain Injuries and Are Associated with Postinjury Behavior

Millions of people suffer mild traumatic brain injuries (mTBIs) every year, and there is growing evidence that repeated injuries can result in long-term pathology. The acute symptoms of these injuries may or may not include the loss of consciousness but do include disorientation, confusion, and/or the inability to concentrate. Most of these acute symptoms spontaneously resolve within a few hours or days. However, the underlying physiological and cellular mechanisms remain unclear. Spreading depolarizations (SDs) are known to occur in rodents and humans following moderate and severe TBIs, and SDs have long been hypothesized to occur in more mild injuries. Using a closed skull impact model, we investigated the presence of SDs immediately following a mTBI. Animals remained motionless for multiple minutes following an impact and once recovered had fewer episodes of movement. We recorded the defining electrophysiological properties of SDs, including the large extracellular field potential shifts and suppression of high-frequency cortical activity. Impact-induced SDs were also associated with a propagating wave of reduced cerebral blood flow (CBF). In the wake of the SD, there was a prolonged period of reduced CBF that recovered in approximately 90 min. Similar to SDs in more severe injuries, the impact-induced SDs could be blocked with ketamine. Interestingly, impacts at a slower velocity did not produce the prolonged immobility and did not initiate SDs. Our data suggest that SDs play a significant role in mTBIs and SDs may contribute to the acute symptoms of mTBIs.

Apnea Associated with Brainstem Seizures in Cacna1a S218L Mice Is Caused by Medullary Spreading Depolarization

Seizure-related apnea is common and can be lethal. Its mechanisms however remain unclear and preventive strategies are lacking. We postulate that brainstem spreading depolarization (SD), previously associated with lethal seizures in animal models, initiates apnea upon invasion of brainstem respiratory centers. To study this, we assessed effects of brainstem seizures on brainstem function and respiration in male and female mice carrying a homozygous S218L missense mutation that leads to gain-of-function of voltage-gated Ca_V2.1 Ca²⁺ channels and high risk for fatal seizures. Recordings of brainstem DC potential and neuronal activity, cardiorespiratory activity and local tissue oxygen were performed in freely behaving animals. Brainstem SD occurred during all spontaneous fatal seizures and, unexpectedly, during a subset of nonfatal seizures. Seizure-related SDs in the ventrolateral medulla correlated with respiratory suppression. Seizures induced by stimulation of the inferior colliculus could evoke SD that spread in a rostrocaudal direction, preceding local tissue hypoxia and apnea, indicating that invasion of SD into medullary respiratory centers initiated apnea and hypoxia rather than vice versa Fatal outcome was prevented by timely resuscitation. Moreover, NMDA receptor antagonists MK-801 and memantine prevented seizure-related SD and apnea, which supports brainstem SD as a prerequisite for brainstem seizure-related apnea in this animal model and has translational value for developing strategies that prevent fatal ictal apnea.SIGNIFICANCE STATEMENT Apnea during and following seizures is common, but also likely implicated in sudden unexpected death in epilepsy (SUDEP). This underlines the need to understand mechanisms for potentially lethal seizure-related apnea. In the present work we show, in freely behaving SUDEP-prone transgenic mice, that apnea is induced when spontaneous brainstem seizure-related spreading depolarization (SD) reaches respiratory nuclei in the ventrolateral medulla. We show that brainstem seizure-related medullary SD is followed by local hypoxia and recovers during nonfatal seizures, but not during fatal events. NMDA receptor antagonists prevented medullary SD and apnea, which may be of translational value.

The metabolic face of migraine - from pathophysiology to treatment

Migraine can be regarded as a conserved, adaptive response that occurs in genetically predisposed individuals with a mismatch between the brain's energy reserve and workload. Given the high prevalence of migraine, genotypes associated with the condition seem likely to have conferred an evolutionary advantage. Technological advances have enabled the examination of different aspects of cerebral metabolism in patients with migraine, and complementary animal research has highlighted possible metabolic mechanisms in migraine pathophysiology. An increasing amount of evidence - much of it clinical - suggests that migraine is a response to cerebral energy deficiency or oxidative stress levels that exceed antioxidant capacity and that the attack itself helps to restore brain energy homeostasis and reduces harmful oxidative stress levels. Greater understanding of metabolism in migraine offers novel therapeutic opportunities. In this Review, we describe the evidence for abnormalities in energy metabolism and mitochondrial function in migraine, with a focus on clinical data (including neuroimaging, biochemical, genetic and therapeutic studies), and consider the relationship of these abnormalities with the abnormal sensory processing and cerebral hyper-responsivity observed in migraine. We discuss experimental data to consider potential mechanisms by which metabolic abnormalities could generate attacks. Finally, we highlight potential treatments that target cerebral metabolism, such as nutraceuticals, ketone bodies and dietary interventions.

Nonepileptic, Stereotypical, and Intermittent Symptoms (NESIS) in Patients With Subdural Hematoma: Proposal for a New Clinical Entity With Therapeutic and Prognostic Implications

BACKGROUND

Transient neurological symptoms (TNS) are frequent in patients with subdural hematomas (SDH) and many will receive a diagnosis of epilepsy despite a negative workup.

OBJECTIVE

To explore if patients with TNS and a negative epilepsy workup (cases) evolved differently than those with a positive EEG (controls), which would suggest the existence of alternative etiologies for TNS.

METHODS

We performed a single-center, retrospective, case-control study of patients with TNS post-SDH. The demographics and clinical and semiological features of cases and controls were compared. The outcome and response to antiepileptic drugs were also assessed and a scoring system developed to predict negative EEG.

RESULTS

Fifty-nine patients with SDH-associated TNS were included (39 cases and 20 controls). Demographic characteristics were comparable in both groups. Dysphasia and prolonged episodes were associated with a negative EEG. Clonic movements, impaired awareness, positive symptomatology, complete response to antiepileptic drugs, and mortality were associated with a positive EEG. Using semiological variables, we created a scoring system with a 96.6% sensitivity and 100% specificity in predicting case group patients. The differences observed between both groups support the existence of an alternative etiology to seizures in our case group. We propose the term NESIS (NonEpileptic, Stereotypical, and Intermittent Symptoms) to refer to this subgroup and hypothesize that TNS in these patients might result from cortical spreading depolarization.

CONCLUSION

We describe NESIS as a syndrome experienced by SDH patients with specific prognostic and therapeutic implications. Independent validation of this new entity is now required.

Dynamic Gain Analysis Reveals Encoding Deficiencies in Cortical Neurons That Recover from Hypoxia-Induced Spreading Depolarizations

Cortical regions that are damaged by insults, such as ischemia, hypoxia, and trauma, frequently generate spreading depolarization (SD). At the neuronal level, SDs entail complete breakdown of ionic gradients, persisting for seconds to minutes. It is unclear whether these transient events have a more lasting influence on neuronal function. Here, we describe electrophysiological changes in cortical neurons after recovery from hypoxia-induced SD. When examined with standard measures of neuronal excitability several hours after recovery from SD, layer 5 pyramidal neurons in brain slices from mice of either sex appear surprisingly normal. However, we here introduce an additional parameter, dynamic gain, which characterizes the bandwidth of action potential encoding by a neuron, and thereby reflects its potential efficiency in a multineuronal circuit. We find that the ability of neurons that recover from SD to track high-frequency inputs is markedly curtailed; exposure to hypoxia did not have this effect when SD was prevented pharmacologically. Staining for Ankyrin G revealed at least a fourfold decrease in the number of intact axon initial segments in post-SD slices. Since this effect, along with the effect on encoding, was blocked by an inhibitor of the Ca²⁺-dependent enzyme, calpain, we conclude that both effects were mediated by the SD-induced rise in intracellular Ca²⁺ Although effects of calpain activation were detected in the axon initial segment, changes in soma-dendritic compartments may also be involved. Whatever the precise molecular mechanism, our findings indicate that in the context of cortical circuit function, effectiveness of neurons that survive SD may be limited.SIGNIFICANCE STATEMENT Spreading depolarization, which commonly accompanies cortical injury, entails transient massive breakdown of neuronal ionic gradients. The function of cortical neurons that recover from hypoxia-induced spreading depolarization is not obviously abnormal when tested for usual measures of neuronal excitability. However, we now demonstrate that they have a reduced bandwidth, reflecting a significant impairment of their ability to precisely encode high-frequency components of their synaptic input in output spike trains. Thus, neurons that recover from spreading depolarizations are less able to function normally as elements in the multineuronal cortical circuitry. These changes are correlated with activation of the calcium-dependent enzyme, calpain.

Photoacoustics can image spreading depolarization deep in gyrencephalic brain

Spreading depolarization (SD) is a self-propagating wave of near-complete neuronal depolarization that is abundant in a wide range of neurological conditions, including stroke. SD was only recently documented in humans and is now considered a therapeutic target for brain injury, but the mechanisms related to SD in complex brains are not well understood. While there are numerous approaches to interventional imaging of SD on the exposed brain surface, measuring SD deep in brain is so far only possible with low spatiotemporal resolution and poor contrast. Here, we show that photoacoustic imaging enables the study of SD and its hemodynamics deep in the gyrencephalic brain with high spatiotemporal resolution. As rapid neuronal depolarization causes tissue hypoxia, we achieve this by continuously estimating blood oxygenation with an intraoperative hybrid photoacoustic and ultrasonic imaging system. Due to its high resolution, promising imaging depth and high contrast, this novel approach to SD imaging can yield new insights into SD and thereby lead to advances in stroke, and brain injury research.